The invention relates to a method and apparatus for the pressure filtration and separation of liquids which contain precipitates, sediment, or other particulate solids. The invention is particularly useful with diagnostic procedures which have heretofore conventionally relied on the necessary use of a centrifugation step, to separate particles from liquid samples being tested, and which is now obviated by the instant invention which uniquely utilizes an in-container pressure filtration system having a three-component filter assembly.
While immunoassay techniques as widely practiced under various protocols are an especially beneficial area of use of the invention, other tests, assays, and filter and separation procedures and techniques requiring centrifugation can benefit from the instant invention.
One such technique is disclosed in U.S. Pat. No. 3,666,854 to Anna Eisentraut. This patent discloses a diagnostic test for the determination of the level of thyroid hormone within a body fluid.
The test includes the steps of adding a radioisotyope labeled hormone to a solution containing a sample of hormone produced within the body and thyro-binding globulin containing bound hormone from the resulting unbound hormone, and counting the radioactivity of either the bound or unbound hormone. This counting procedure will indirectly indicate the amount of endogenous hormone which is bound to the natural globulin and protein bonding sites within the blood. The separation of the free hormones from hormones bound to natural binding sites is carried out by sorption of the free hormones by particulate inorganic crystalline lattice material which is preferably in colloidal form. Once sorption is complete, the material is centrifuged to separate the colloid from the resulting solution, for example, at 2,400 rpm for 5 minutes. The colloidal material is then packed in the bottom of the tube and counted on a scintillation well counter to determine the amount of hormone present.
Various in-tube filter-type separation devices are taught in earlier patents, and to which reference may be had to illustrate avenues of development which differ from that of the present invention.
Thus, U.S. Pat. No. 3,693,804 to Grover discloses a pressure differential sampling apparatus utilizing an elongate hollow piston member having a central axial bore and a flexible peripheral lip which engages the inside wall of the test tube, allowing pressure to be formed in the sample space, and wherein the filtrate is received through a single-element filter and retained within the interior of the elongate piston member.
U.S. Pat. No. 4,189,385 to Greenspan is directed to a method and apparatus for separating serum or plasma from the heavier formed elements of the blood wherein a collection tube is filled with a previously centrifuged sample, and a separator tube having a valving plug is then inserted down through the sample which passes through the valve plug into the separator tube for collection.
U.S. Pat. No. 4,254,082 to Schick teaches a method for determining a specific binding substance in an assay test, and provides an absorbent, such as ion-exchange materials, cellulose, silica gel and other materials capable of nonspecific binding with the substance to be determined, retained between two porous discs wherein the absorbent is contacted with the test sample, separated from the unabsorbed portions of the sample, contacted with the labeled binding partner, then measured for radioactivity.